Applications of UV/H2O2, UV/persulfate, and UV/persulfate/Cu2+ for the elimination of reverse osmosis concentrate generated from municipal wastewater reclamation treatment plant: Toxicity, transformation products, and disinfection byproducts

Abstract

Reverse osmosis concentrate (ROC) resulting from treatment of municipal wastewater reclamation involves high concentrations of recalcitrant pollutants. This study evaluated the toxicity of an ROC containing harmful biocides during representative UV synergistic oxidation processes (SOPs) (e.g., UV/hydrogen peroxide (H2O2), UV/persulfate (PS), and UV/PS/Cu2+). Treated ROC exhibited up to 1.3–2.3 times higher toxicity than the parent compounds such as dodecyl trimethyl ammonium chloride (DTAC) and dodecyl dimethyl benzyl ammonium chloride (DDBAC). Based on the intermediates identification, the major toxic intermediates were screened through silico assessment using the quantitative Ecological Structure-Activity Relationship (ECOSAR) tool. The transformation products (TPs) of hydroxylation and ketonization were the major formed reactions from the UV/PS/Cu2+. Also, some cytotoxic TPs were accumulated during the UV/H2O2 and UV/PS oxidations, where the carbonaceous-disinfection byproducts were more than the nitrogenous-disinfection byproducts. In the presence of chloride and bromide, chlorate and bromate could be formed during the UV-SOP; they were influenced by the different water matrix in comparison with the different ROC. Also, the formation of the total organic halogen species (TOX) was found to follow this order: UV/PS/Cu2+ < UV/H2O2 < UV/PS. In this study, the predicted cytotoxicity using the correlation between the TOX and the cytotoxicity was more acceptable than that of the cytotoxicity index method. Further, the R-square of the correlation between the TOX and the cytotoxicity for the UV/H2O2 and UV/PS was 0.82 and 0.79, respectively. The predicted cytotoxicity using the TOX correlation method in the ROC could also be used to monitor and prevent the application of different oxidations in municipal wastewater reclamation treatment plants.